1. Field of the Invention
The present invention relates to a zoom lens system and an electronic imaging apparatus using such a zoom lens system.
2. Description of Related Art
In recent years there has been an increasing demand for a zoom lens system in an electronic imaging apparatus, such as a digital camera, etc., to be more compact (miniaturized) and to have higher optical performance. Furthermore, there has been an increasing demand to reduce the size (miniaturize) and weight of the focusing lens group to carry out a rapid and quiet focusing operation, in order to carry out a desirable movie shooting (video recording) operation. Furthermore, there is also an demand for the field curvature that occurs during a zooming operation to be to favorably corrected.
Japanese Unexamined Patent Publication Nos. 2000-28923 and 2010-175954 disclose a zoom lens system configured of a positive first lens group, a negative second lens group, and a positive rearward-remaining lens group, in that order from the object side, in which the second lens group is divided into a negative front sub-lens group and a negative rear sub-lens group, and the negative rear sub-lens group constitutes a focusing lens group that is moved in the optical axis direction when carrying out a focusing operation.
However, in the zoom lens system taught in above-mentioned Japanese Unexamined Patent Publication No. 2000-28923, since the rear sub-lens group of the second lens group (the rear sub-lens group L2b in Japanese Unexamined Patent Publication No. 2000-28923), which constitutes a focusing lens group, is configured of two negative lens elements and one positive lens element, i.e., three lens elements, miniaturization and reduction in weight of the focusing lens group is insufficient, so that a rapid and quiet focusing operation cannot be carried out.
Furthermore, in the zoom lens system taught in above-mentioned Japanese Unexamined Patent Publication No. 2010-175954, since the lens group provided behind the second lens group (the “third lens group G3” in Japanese Unexamined Patent Publication No. 2010-175954), which constitutes a focusing lens group, is configured of a single lens element, there is no problem in regard to the reduction in size and weight of the focusing lens group, however, since the lens group (third lens group) provided behind the second lens group also serves as a compensation lens group that compensates for the image-plane position during zooming, fluctuation in field curvature occurs during zooming.